usb: host: xhci-rcar: Simplify getting the firmware name for R-Car Gen3

This patch simplifies getting the firmware name for R-Car Gen3.
Almost all R-Car Gen3 USB3.0 Host controllers use "V3". But,
r8a7795 ES1.x SoCs only should use "V2". Since the xhci-plat already
has the firmware_name of R-Car Gen3 as "V3", the xhci-rcar doesn't
need some members of rcar_quirks_match.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>